Qt-interest Archive, August 2006
[Qt3] Compression of mouse motion events (bug?)
Message 1 in thread
I have an opengl application where I use the mouse to draw a freehand
curve. If the application is slow to render I only get very coarse mouse
motion events, which means the freehand curve doesn't follow the mouse
as precisely as it could. I can see in qapplication_x11.cpp:4016-4036
(qt-x11-free-3.3.6) that Qt compress mouse move events and toss out the
lot except the very last one, so I have Qt to thank for this problem :-)
I don't understand why such compression is hardcoded in Qt - why not
instead do one of the following
1) translate all MotionNotify events into QEvent::MouseMove events. Note
in a flag whether the mouse event could have been compressed/ignored,
ie: QMouseEvent::ignorable();
2) Alternatively, keep compressing several MotionNotify events into a
single QMouseEvent, but record intermediate positions and make them
available e.g. like this: std::vector<QPoint>
QMouseEvent::compressedPositions()/compressedGlobalPositions();
Best regards,
Thomas
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Message 2 in thread
Hi,
> I don't understand why such compression is hardcoded in Qt - why not
> instead do one of the following
Because the following is probably of no interest to the majority of Qt
users. Is the compression really hard-coded in a way that cannot be
overridden? I haven't really looked at it, but I suspect one of these
approaches may give access to uncompressed events:
http://doc.trolltech.com/3.3/qapplication.html#notify
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Message 3 in thread
Dimitri wrote:
> Hi,
>
>> I don't understand why such compression is hardcoded in Qt - why not
>> instead do one of the following
>
> Because the following is probably of no interest to the majority of Qt
> users. Is the compression really hard-coded in a way that cannot be
> overridden? I haven't really looked at it, but I suspect one of these
> approaches may give access to uncompressed events:
> http://doc.trolltech.com/3.3/qapplication.html#notify
>
> --
> Dimitri
They are accessible, but not in a platform independent way. I override
both x11Event and mouseMoveEvent. In x11Event I record all the
MotionNotify events and in mouseMoveEvent I process them. Hopefully my
app will never need to run on Windows ;-)
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